HP aC++/HP C A.06.20 Programmer's Guide

10 Mixing C++ with Other Languages
This chapter provides guidelines for linking HP aC++ modules with modules written
in HP C and HP FORTRAN 90 on HP 9000 Series 700/800 systems. It discusses the
following topics:
• “Calling Other Languages” (page 245)
• “Data Compatibility between C and C++” (page 245)
• “HP aC++ Calling HP C” (page 246)
• “HP C Calling HP aC++” (page 249)
• “Calling HP FORTRAN 90 from HP aC++” (page 251)
Calling Other Languages
A module is a file that contains one or more variable or function declarations, one or
more function definitions, or similar items logically grouped together. Mixing modules
written in C++ with modules written in C is relatively straightforward since C++ is for
the most part a superset of C. Mixing C++ modules with modules in languages other
than C is more complicated.
When creating an executable file from a group of programs of mixed languages, one
of them being C++, you must be aware of the following:
• In general, the overall control of the program must be written in C++. In other
words, the main function should appear in a C++ module and no other outer block
should be present.
• You must pay attention to case sensitivity conventions for function names in the
different languages.
• You must make sure that the data types in the different languages correspond. Do
not mismatch data types for parameters and return values.
• Storage layouts for aggregates differ among languages.
• You must use the extern "C" linkage specification to declare modules that are
not written in C++; this is true whether or not the module is written in C.
• You must use the extern "C" linkage specification to declare modules that are
written in C++ and called from other languages.
• Do not use extern "C" when you include standard C header files because these
header files already contain extern "C" directives.
NOTE: HP aC++ classes are not accessible to non-C++ routines.
Data Compatibility between C and C++
Many of the data types between C and C++ are identical as C++ is, for most part, a
superset of C. Both languages support char, short, int, long, float, and double
Calling Other Languages 245